Tire building machines heretofore have been known to employ a finger ply-down, bead setter and bladder turn-up at each axial end of a tire building drum. After ply material is applied in cylindrical fashion on the drum with the edges thereof extending axially beyond the ends of the drum, the ply downs are indexed axially towards the drum and operated to turn or fold the ply edges down over respective ends of the drum. Then tire beads are pressed into place against the turned down ply edges at the drum ends by the bead setters which include bead setting rings or the like for holding the beads centered therein during bead placement. Once the beads have been set in place, the tackiness of the uncured ply material is relied upon to hold the beads in place at the drum ends as the bead setters and ply downs are axially retracted away from the drum for subsequent turn-up and stitching of the ply edges around the beads by the bladder turn-ups.
While such machines generally perform satisfactorily, some problems exist in connection therewith. For example, any off center (axis) misalignment of the bead setters with respect to the tire building drum or machine axis will result in out of register placement of the beads at the ends of the drum both with respect to the drum as well as each other. Such misalignment may result from normal wear tolerances of the bead setters or from misadjustment of the bead setting rings. Moreover, the bead setting rings typically are supported in cantilever fashion when fully extended for bead placement whereby any play or flexing of the cantilever support may result in off center placement of the beads at the drum ends. In any event, the beads held only by the tackiness of the ply material may move off center during the turn-up operation.
Another problem is that initial progressive wrapping of the tire ply material at the inner diameter of the bead by the bladder turn-up may not be as tight as desired especially when the ply material is particularly stiff as in the case of wire, dual cross ply aramids or cross-woven nylons. Such initial wrapping usually occurs before full inflation of the turn-up bladder or bladders and hence before attainment of full wrapping and pressing forces. Consequently, proper material flow may not be obtained and air entrapment may occur.